I tried installing J-Link 6.40 on a fresh Ubuntu 18.04.1 VM, this also exhibits the doubling. Going back a few versions, it appears the last working version for me is 6.32i, 6.34 and later show the doubling.

For the following, I'm using: J-Link tools V6.41a on Ubuntu 18.04
I have reproduced in multiple configurations:
Using a Nordic PCA10040 (nrf52832 dev board) with on-board J-Link, I can erase, start JLinkExe, start JLinkRTTClient, and any input is…

With recent versions of JLinkRTTClient every keyboard input appears doubled. With an older version of the software (6.18d) I do not see this issue. I am seeing this when using RTT with several different SDKs (Nordic nrf5 v12, v15, and zephyr). The…